Field of the Invention
The invention relates to a method for emulating a three-phase brushless DC motor using a load emulator, wherein the load emulator is connected in a three-phase manner via its load terminals to the supply terminals of a motor controller, and the load emulator has emulator power electronics and an emulator controller for controlling the emulator power electronics, wherein the emulator controller determines the supply terminals that are driven by the motor controller and the supply terminals that are not driven, and the emulator power electronics are driven by the emulator controller in such a manner that phase currents iemulate calculated by the emulator controller on the basis of a motor model flow in the supply terminals that are driven by the motor controller, and a phase voltage vemulate calculated by the emulator controller on the basis of a motor model is applied to the supply terminal that is not driven by the motor controller. Moreover, the invention also relates to the emulator controller of a load emulator that is configured such that it can carry out the above-described method for emulating a three-phase brushless DC motor in conjunction with emulator power electronics.
Description of the Background Art
Methods for emulating electrical loads with the aid of load emulators are used for testing motor controllers under laboratory conditions without the need to connect a physical electric drive—here in the form of a three-phase brushless DC motor—to the controllers. The electrical load, which is to say the three-phase brushless DC motor, is instead emulated by the load emulator. The motor controller typically has a control unit with a power output stage in the form of a converter. The control unit generates converter control data that are used to appropriately drive the power switches of the converter, which typically are implemented by semiconductor switching elements (IGBT, IGCT, etc.). In the application case under consideration here, the converter of the motor controller operates as an inverter, which is to say it has a DC voltage source as the energy source and drives a load with AC voltage.
The load emulator is oftentimes implemented in the form of a hardware-in-the-loop simulator, which is to say by a simulation computer that calculates mathematical models of the environment to be simulated—here, the load in the form of the brushless DC motor—using numerical methods and that for its part has a power electronic output stage—the emulator power electronics—that can be connected through the load terminals of the load emulator to the corresponding supply terminals of the motor controller. The method for emulating a three-phase brushless DC motor implemented on the load emulator ultimately ensures that the motor controller is electrically loaded through its supply terminals as if it were connected to the real drive.
Brushless DC motors operate like permanently excited three-phase synchronous machines and have low wear and low maintenance on account of their brushless construction. In the industrial realm, such as in the automotive industry for example, brushless DC motors are often used as drives for auxiliary equipment such as, e.g., pump drives (oil, fuel) and actuating drives (variable-speed transmissions, clutches, headlight range adjusters, valves/flaps).
In brushless DC motors driven in block commutation mode, two of the three motor phases are always driven by the motor controller—two of the three supply terminals of the motor controllers are then driven—and the third phase of the three-phase winding is not driven by the motor controller; the corresponding supply terminal of the motor controller is then likewise not driven. A rotating magnetic field is created through periodic switching of the three-phase windings by the motor controller. In the phase of the brushless DC motor that is not driven by the motor controller, the phase current drops, and soon vanishes completely. The phase of the brushless DC motor that is not driven is often referred to as the currentless phase, wherein—as explained above—the states of not being driven and of being currentless can be separated in time. If a phase of the brushless DC motor is no longer driven by the motor controller, the consequence is that the phase current in the phase that is no longer driven ultimately vanishes, but not necessarily immediately after commutation, and the phase is then in fact currentless.
In the phase of the brushless DC motor that is not driven, however, a back EMF is induced, the sensing of which is of major importance for driving the brushless DC motor, since the angular position of the rotor can be determined therefrom, and hence the motor controller can determine the time of the next commutation, which is to say the switch from non-driven to driven supply terminals and vice versa, even without a separate rotary position sensor. For this reason, the emulation of the back EMF induced in the non-driven phase is essential in emulating brushless DC motors that are driven in block commutation mode so that the motor controller can determine the time of the next commutation even without a rotary position sensor. However, calculation of the back EMF as part of emulation is important even in the case of brushless DC motors equipped with a rotary position sensor, since only in this way can the physical relationships of the emulated motor, and thus the connected loads, be correctly calculated and emulated.
In order to apply appropriate connected electrical loads to the supply terminals of the motor controller, the emulator power electronics include voltage sources and current sources, which can generally be connected to the load terminals of the emulator power electronics through decoupling inductances. Thus, by suitably connecting the voltage sources and current sources to the load terminals of the emulator power electronics it is possible to react to whether a load terminal only has an induced back EMF connected to it in the state in which it is not driven by the motor controller, or whether a load terminal carries a current in the state in which it is driven by the motor controller. The decoupling inductances provided between the load terminals and the voltage and current sources prevent the connected electrical loads defined by the switched voltage and current sources from exerting an undelayed effect on the load terminals.